The present disclosure relates to implantable prosthetic heart valves. More particularly, it relates to prosthetic heart valves incorporating a stent and methods of compressing stented prosthetic heart valves for loading into a delivery system.
Various types and configurations of prosthetic heart valves are used to replace diseased natural human heart valves. The actual shape and configuration of any particularly prosthetic heart valve is dependent to some extent upon the valve being replaced (i.e., mitral valve, tricuspid valve, aortic valve, or pulmonary valve). In general, the prosthetic heart valve designs attempt to replicate the function of the valve being replaced and thus will include valve leaflet-like structures used with either bioprosthesis or mechanical heart valves prosthesis. As used throughout the specification, a “prosthetic heart valve” is intended to encompass bioprosthetic heart valves having leaflets made of a biological material (e.g., harvested porcine valve leaflets, or bovine, equine, ovine or porcine pericardial leaflets, small intestinal submucosa), along with synthetic leaflet materials or other materials.
Stented bioprosthetic heart valves have a frame (or stent) to which the biological valve material is attached. The biological valve members are sutured to the stent that provides support for the valve member in the patient's body. The stent prevents the biological valve members from collapsing and simplifies the insertion of the valve into the annulus of the patient after excision of the diseased valve. The stented bioprosthetic valve imitates the natural action of heart valves and provides a structure that is relatively compatible with the cardiovascular system. Stented prosthetic heart valves are believed to have important clinical advantages over mechanical or non-tissue prosthetic valves.
For many percutaneous delivery and implantation systems, the stent frame of the valved stent is made of a self-expanding material and construction. The stent frame is made of nitinol (a nickel and titanium alloy). With these systems, the valved stent is crimped down to a desired size and held in that compressed arrangement within an outer sheath, for example. Retracting the sheath from the valved stent allows the stent to self-expand to a larger diameter, such as when the valved stent is in a desired position within a patient.
Typically a stented transcatheter valve having a self-expanding frame, such as a nitinol based frame, is cooled prior to loading into the delivery system. The cooling process brings the valve out of the austenitic and into the martensitic phase. While in the martensitic phase, nitinol is more malleable. Often an ice bath based solution of approximately 4° C. is employed in order that the nitinol frame enters the martensitic state and becomes malleable and can be compressed for loading to a delivery system. In some stented transcatheter valves, the tissue used in the valve is in a “dry” state and is processed using glycerine, alcohols, other chemicals, and combinations thereof rather than a “wet” state and processed with excess glutaraldehyde. In valves including “dry” tissue, it is desirable to maintain the tissue in a dry state and avoid processes that use aqueous or liquid solutions. For dry tissue loaded onto a nitinol based frame or other self-expanding frame, it is desirable to cool the frame to a malleable, collapsible, state without exposing the tissue to an aqueous solution.